【摘要】 确定了在pH 5.2到8.7和温度22°到45℃时钼铁蛋白和铁蛋白的稳定性。按logKm和logV分别对pH作图,得到下列参数。于30℃在酸性侧,乙炔络合常数PK_b（C₂H₂）=6.43—6.50,乙炔催化常数pK_b′（C₂H₂）=4.78,在碱性侧乙炔络合常数pK_a（C₂H₂）=7.42—7.55,乙炔催化常数pK_a′（C₂H₂）=7.88—8.29,氮络合常数pK_a（N₂）=7.75—7.9及氮催化常数pK_a′（N₂）=8.08—8.68。既然pK_a与pK_b或pK_a′与pK_b′二者间隔小于3.5个单位,又按V/Km及V′对pH作图,其结果为pKb（C₂H₂）=6.28pK_a（C₂H₂）=7.68和pK_b′（C₂H₂）=5.53和pK_a′（C₂H₂）=8.93。将不同温度下的pK_b或pK_a分别对各自温度的倒数作图,其热力学数据为由pH 5.7到7.3范围内,质子移变基团的解离热⊿H（ioh）=7742卡/克分子,相应的pK_b（C₂H₂）=6.16—6.36;由pH 7.3到8.4范围内⊿H_ion=6983卡/克分子,相应的pK_a=8.24—8.44。这些数据指出固氮酶钼铁蛋白络合乙炔的功能基团可能具有咪唑基·巯基和氨基相类似的结构,这种推测正在用化学修饰的方法加以验证。更多还原

【Abstract】 The stabilities of Mo-Fe-protein and Fe-protein are determined at pH’s between 5.2 and 8.7 and temperature between 22℃ and 45℃. By plotting log Km and log V, respectively, versus pH values the following values of the parameters are obtained. Under temperature of 30℃ on the acidic side, C₂H₂-binding constant pK_b（C₂H₂）=6.43—6.5 and C₂H₂-catalyzing constant pK_b’（C₂H₂）=4.78, while on the alkaline side, C₂H₂—binding constant pKa （C₂H₂）=7.42-7.55, C₂H₂-catalyzing constant pK_α’（C₂H₂） = 7.88-8.29, and N₂-binding constant pK_α （N₂）=7.75-7.9, N₂—catalyzing cnstant pK_α’ （N₂）=8.08-8.68. Since pK_α and pK_b or pK_a’ and pK_b’ are separated by less than 3.5 units, with graphic plotting of V/K_m and V against pH values, the results obtained are: pK_b （C₂H₂）=6.28, pK_α （C₂H₂）=7.68 and pK_b’（C₂H₂）=5.53, pK_α’ （C₂H₂）=8.93. By plotting pK_b or pK_α, respectively at different temperatures versus the reciprocal of temperature, the thermodynamic data are: for a pH range between 5.7 and 7.3, the change in dissociation heat content of prototropic group △H_ion = 7742 cal mol^-1 with corresponding pK_b = 6.6-6.36, while for a pH range between 7.3 and 8.4, △H_ion=6983 cal mol^-1 with corresponding pK_α = 8.24-8.44. These data reveal that the functional group of nitrogenase Mo-Fe-protein for C₂H₂ binding is probably similar in structure to imidazole group, sulfhydryl group and amino group. This prediction is being examined with chemical modification method by us.更多还原